A pair of interacting galaxies might be
experiencing the galactic equivalent of a mid-life crisis. For some reason, the
pair, called Arp 82, didn't make their stars early on as is typical of most
galaxies. Instead, they got a second wind later in life – about 2 billion
years ago – and started pumping out waves of new stars as if they were
young again.

The new observations are from NASA's
Galaxy Evolution Explorer, NASA’s Spitzer Space Telescope and the Southeastern
Association for Research in Astronomy Observatory at Kitt Peak, Ariz.

Arp 82 is an interacting pair of
galaxies with a strong bridge and a long tail. NGC 2535 is the big galaxy and
NGC 2536 is its smaller companion. The disk of the main galaxy looks like an
eye, with a bright “pupil” in the center and oval-shaped “eyelids.”Dramatic “beads on a string” features
are visible as chains of evenly spaced star-formation complexes along the
eyelids. These are presumably the result of large-scale gaseous shocks from a
grazing encounter.The colors of
this galaxy indicate that the observed stars are young to intermediate in age,
around 2 million to 2 billion years old, much less than the age of the universe
(13.7 billion years).

The pair first burst with new star
formation about 2 billion years ago after swinging by each other. A second
close passage more recently resulted in yet another batch of star formation.

The puzzle is: why didn’t Arp 82 form
many stars earlier, like most galaxies of that mass range? Scientifically, it
is an oddball and provides a relatively nearby lab for studying the age of
intermediate-mass galaxies.

In more popular terms, think of this
as an example of arrested development. For some reason, it took a
kick-in-the-pants to get the stars forming recently, whereas most other
galaxies of that mass range formed their stars much earlier (between 4 and 8
billion years ago).

A journal article with a detailed analysis
of these data has been accepted by the Astronomical Journal. This research has been sponsored by NASA.

The California
Institute of Technology in Pasadena, Calif., leads the Galaxy Evolution
Explorer mission and is responsible for science operations and data analysis.
NASA's Jet Propulsion Laboratory, also in Pasadena, manages the mission and
built the science instrument. The mission was developed under NASA's Explorers
Program managed by the Goddard Space Flight Center, Greenbelt, Md. Researchers
sponsored by Yonsei University in South Korea and the Centre National d'Etudes
Spatiales (CNES) in France collaborated on this mission.